Thank you for the link. However, it's not clear whether that law merely covers pretending to be someone's SO, or covers other types of trickery, such as when a woman falsely tells a date she's single or a man says he's two inches taller than he really is. I think we can agree that if I lie about my height, it does not remove consent.
Secondly, I don't think your example about boxing holds up. Being punched in the face is not an active action--it is passive. The only way someone actively participates in getting punched in the face is by forcefully slamming their head into someone's hand, and in that case, they surely consented by their action.
I'll say it again. Sex is not a contract. Hugging is not a contract. Helping someone carry a box is not a contract. Sitting down on a chair is not a contract.
I think there should be laws to cover this sort of situation. It would still not be rape--it's more like theft of services or failure to perform one's end of an agreement. (She fully consented, but it was part of a larger agreement, and that larger agreement was fraudulent, not the sex.)